In a redundant power supply system, two or more power supply modules (power converters that convert electrical power from one form into another) have respective outputs connected in parallel to a single load via a common bus. Each power supply module has an associated ORing element (or switch), typically a field-effect transistor (FET) device, disposed between the output node of each module and the load. The ORing switches are operable to selectively couple or decouple the respective power supply module from the load, thereby effectively isolating current generated at the corresponding module from passing to the common bus. Similarly, each respective power supply module may have an associated input switch connecting the module to a power source. The respective switches are controlled to decouple associated power supply modules from the load and/or the power source upon detection of one or more of deficient operating conditions, each representing a failure occurring, or sub-optimal performance occurring in the system. The architecture of each respective power supply module of the system provides for a control circuit to direct the operation of the respective switches upon detection of one or more of these conditions. This may be referred to as “active ORing.”
Active ORing does have draw-backs. A FET, when it is turned on, allows current to flow in either direction through its channel. If an input power source fails due to a short circuit, a large reverse current will be induced and will be allowed to flow through an ORing FET as long as its gate is enhanced. If the common bus is exposed to an input fault for a prolonged period of time, the bus voltage will discharge, thus bringing down the system. Because of this possibility, reverse current is one common operating condition that a power supply module monitors for. It is desirable that the active ORing solution is both accurate and capable of extremely fast detection of reverse current fault conditions. Once the fault has been detected, a controller is required to turn off the ORing FET as fast as possible, and thus, in turn, isolate the input fault from the common bus and prevent any further reverse current.
Similarly, if a short occurs within the power supply module, excessive current may be pulled down from an input bus (connecting the power source), via an input FET. Excessive forward current at the input FET is another operating condition monitored for, and if detected, the controller turns off the input FET.
Other common operating conditions that are monitored by the respective power supply modules include under-voltage (UV) conditions and over-voltage (OV) conditions. These are defined to be the limits within which the ORing switch and components of the system will properly operate. Such protections ensure that only a faulty power supply module or modules are isolated from the load, where, for example, a number of power supply modules are operating to provide voltage to the common bus.